1. Field of the Invention
The invention relates to a plant for the thermal treatment of waste materials, having a grate which is formed by grate blocks and on the surface of which the waste materials lie for the thermal treatment, the grate having gas passages which are connected to a gas supply for the grate surface. Furthermore, the invention relates to a grate block for such a plant.
2. Discussion of the Prior Art
A plant of the type mentioned at the beginning has been disclosed, for example, by DE 40 27 908 A1, DE 196 50 119 C1 or EP 0 621 448 B1. In this known plant, in which waste materials in particular are incinerated, oxygen is added to the primary air flowing into the undergrate chamber in order to obtain as far as possible low-pollution combustion of the fuels. Furthermore, on account of the oxygen requirement of different magnitude in various regions of the grate, it is known to vary the oxygen content of the primary air.
In order to distribute the oxygen to the grate in accordance with the oxygen-requirement profile, an appropriate number of undergrate chambers, into which primary air of different oxygen content flows, are provided in the known incineration plant. So that the desired oxygen profile is retained, however, mixing of the primary air enriched with oxygen must be prevented during the discharge from the various undergrate chambers. Furthermore, the primary air must not be enriched too highly with oxygen, since otherwise combustion residues, also called riddlings, falling into the undergrate chamber, are undesirably ignited. At the same time, an adequate volumetric flow of primary air must flow into the undergrate chamber so that, on the one hand, the grate is cooled and, on the other hand, the risk of combustible gases diffusing back from the combustion space into the undergrate chamber at a primary-air volumetric flow which is too low is removed, these gases forming an explosive mixture with the added oxygen in the undergrate chamber.
Based on this prior art, the object of the invention is to provide a plant for the thermal treatment of waste materials, or a grate block for a plant, which permits a specific oxygen feed and does not have the disadvantages of the known plants.
Various advantages are obtained by the feeding of oxygen without mixing with the undergrate directly at the location where oxygen is required at the grate surface. Thus, the restrictions for the incineration plant due to the restricted number of undergrate chambers do not apply. The latter no longer need to be sealed off from one another if locally different oxygen concentrations are desired. The ignition of riddlings is avoided, since there is only air in the undergrate chamber. The plant may therefore be run with a smaller undergrate volume. Since, according to the invention, pure oxygen can be fed, both combustion and degassing can be carried out at a higher temperature.
In the invention, only primary air flows through the undergrate chamber, whereas the additional oxygen necessary for low-pollution combustion is not fed until the point of action, at the end face, in the immediate vicinity of the grate surface on which the combustion or degassing of waste materials takes place. As a result, it is possible to specifically set the oxygen content of the combustion air in accordance with the respective requirement. Furthermore, it is no longer necessary to design different undergrate chambers which are intended to influence the oxygen content of the combustion air in known incineration plants, as a result of which corresponding supply arrangements for the primary air are also dispensed with, so that the requisite technical outlay in the case of the incineration plant according to the invention is lower compared with known combustion plants.
Thus, it is proposed to define a plurality of successive regions with in each case at least one discharge opening in a predetermined direction on the grate, in which case the volumetric oxygen flow discharging from the discharge opening of each region can be regulated. Due to this subdivision of the grate into various regions and the specific regulation of the volumetric oxygen flow, very accurate setting of the oxygen content of the combustion air is possible, as a result of which the amount of oxygen fed can be optimized at any point. In this embodiment of the plant according to the invention, it is especially advantageous if the discharge openings formed in one region are connected to a common section of the oxygen feed system for the gas supply.
A plurality of nozzles, which have the discharge openings for the oxygen to be fed, are preferably connected to the end of the oxygen feed system of the gas supply. At the same time, it is especially advantageous if, at an incineration grate, in each case at least one nozzle is assigned to at least one of the primary-air passages, so that oxygen can be specifically fed to the primary air flowing through this primary-air passage. In particular, it is of advantage if the nozzle is in arranged and held in the primary-air passage. In this way, the nozzle, which heats up during the combustion of the fuels, is cooled by the primary air flowing into the primary-air passage. This effect is intensified if the nozzle is held in the primary-air passage in a heat-conducting manner, so that the heat quantity stored in the nozzle can be rapidly dissipated to the grate.
Furthermore, it is of advantage if the nozzle is designed in such a way that the oxygen discharging from the nozzle discharges approximately at sound velocity. In this way, obstructions of the nozzle are avoided on the one hand, and the nozzle is additionally cooled by the oxygen due to its high flow velocity on the other hand.
In a preferred embodiment of the plant, the oxygen feed system of the gas supply can be additionally connected to a second gas supply, by means of which a gas which is more inert compared with oxygen can be fed to the discharge openings. By means of this second gas supply, flow (also) occurs through the nozzles, if no 02 is fed, in order to avoid obstructions.
Furthermore, it is also proposed to provide a further oxygen supply for the oxygen enrichment of the primary air during the combustion in order to ensure a sufficient oxygen content of the combustion air.
In a further preferred embodiment of the plant according to the invention for the incineration of waste materials, at least one grate element, which is formed from a plurality of grate blocks arranged side by side in a predetermined direction and provided in each case with at least one primary-air passage, is assigned to each undergrate chamber. In this case, at least one of the discharge openings is provided on every grate block of a predetermined number of grate blocks, for example on every second grate block. If two or more grate elements are formed in an incineration plant, it is especially advantageous if the zones are provided with grate blocks of a identical design, the discharge openings of in each case grate blocks arranged side by side transversely to the predetermined direction being connected to a common section of the feed system of the gas supply. In this way, the elements arranged side by side can be subdivided in the predetermined direction into various regions which are supplied with different oxygen quantities by the various sections of the oxygen feed system.
Since the waste materials, in the plant according to the invention, are fed continuously, they are also conveyed continuously forward and are incinerated or degassed in the process. On account of the decreasing oxygen requirement toward the end of the grate, the oxygen supply as viewed in the transport direction of the waste materials is specifically reduced in accordance with the requirement.
To transport the waste materials, grate blocks of the grate are arranged so as to be staggered one behind the other and inclined at an angle in the predetermined transport direction, the grate blocks forming bearing edges, running transversely to the predetermined transport direction, for the fuels. Some of the grate blocks are mounted so as to be movable between an initial position and a lifting position. The fuel is transported continuously along the grate surface by the movement of the grate blocks. The discharge openings for oxygen according to the invention are preferably provided on the fixed grate blocks, since a complicated feed system, which otherwise would have to permit the movement of the grate blocks, can be dispensed with.
The grate blocks of the plant according to the invention are cooled in order to prevent premature aging due to high temperatures caused by the use of oxygen.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.